The invention concerns a method for operating a blister packaging machine, wherein a bottom sheet provided with cup-shaped recesses is combined with a top sheet in or upstream of a sealing station, and is guided at a constant transport speed V through the sealing station, wherein the sealing station contains a sealing roller, which can be temperature-controlled, for sealing the top sheet onto the bottom sheet, and wherein the transport speed V can be preselected in an at least indirect manner.
The invention also concerns a corresponding blister packaging machine.
A blister packaging machine of conventional structure comprises a forming station, in which a plurality of cup-shaped depressions are formed into a bottom sheet, which consists of plastic material or aluminium, into which a product, e.g. a pharmaceutical tablet, is inserted in a downstream filling station. After product supply, the bottom sheet is fed to a sealing station. A cover sheet is introduced directly before or within the sealing station and disposed on the bottom sheet. The cover sheet is tightly sealed onto the bottom sheet within the sealing station using heat, thereby enclosing the product in the cup-shaped depression.
The forming station is operated in cycles and therefore discontinuously. The sealing station can also be operated in cycles or, alternatively, continuously, wherein conventional compensation means effect transfer between cyclical operation of the forming station and continuous operation of the sealing station.
The invention concerns a continuously operated sealing station which usually utilizes a sealing roller which can be controlled to a predetermined desired temperature using a heating device. The bottom sheet is transported, together with the cover sheet, at a constant transport speed V through the sealing station i.e. through the gap between the sealing roller and a counter roller, wherein heat is transferred from the sealing roller to the sheets, thereby connecting them.
Heat transfer between the sealing roller, which is kept at a constant temperature, and the sheets depends on the transport speed V. At high transport speeds, the contact time between the sealing roller and the sheets is relatively short, and only a small amount of heat can be introduced into the sheets. If insufficient heat is introduced into the sheets, the sealing may be incomplete and the bottom sheet and cover sheet might not be tightly sealed. At slow transport speeds, the contact time between the sealing roller and the sheets is relatively long and a large amount of heat is consequently introduced into the sheets which could cause damage to the relatively heat-sensitive cover sheet. Proper sealing between the bottom sheet and the cover sheet is also not ensured in this latter case.
To prevent the above-mentioned problems in a conventional blister packaging machine, before operation start, the packaging machine is set to a desired optimum cycle rate or to a sheet transport speed which is directly proportional thereto, and a corresponding sealing roller temperature.
If a lower cycle rate or transport speed is temporarily desired for production reasons, the packaging machine is stopped and the user adjusts the reduced cycle time. Moreover, the user tries to determine and adjust a suitable temperature setting for the sealing roller from his/her experience. This method is very cumbersome and requires specially trained personnel. Practice has shown that, through trial and error, a substantial amount of time is needed to find a suitable temperature for the sealing roller to match the reduced cycle time. In the meantime, the packaging machine is inoperative. This is highly uneconomical.
It is the underlying purpose of the invention to provide a method for controlling a blister packaging machine for changing the transport speed of the sheets or the cycle time and the temperature of the sealing roller in a rapid and coordinated manner. Moreover, a blister packaging machine shall be provided which facilitates performance of the method.